Carbon yarn products are used in many applications such as in the preparation of carbonized fabrics for composite reinforcement and the like. An example of a carbonized fabric is found in U.S. Pat. No. 972,110. Often, a number of carbon-based filaments are bound together such as by twisting, to form a yarn element. Individual yarn elements are then further processed such as by twisting a number of elements to form a cord, or weaving the elements to form a cloth or fabric.
In industries using carbonizable yarn, such as carbonized fabric industries or the like, the first step in manufacturing the carbon yarn is to remove any sizing materials such as starch, mineral oil, wetting agents or "surfactants" or the like, from the raw yarn. This procedure is known as "scouring" and usually includes cleaning the yarn with a dry cleaning solvent such as perchloroethylene or another similar scouring agent. Sizing materials are often applied to carbonizable filaments during the formation of the yarn products to prevent damage during subsequent processing to prepare the yarn. Such subsequent processing may include twisting, spooling, weaving or the like. The sizing material is applied to the yarn product to help prevent damage during such processing.
However, if the sizing is not removed from the carbonizable yarn prior to carbonizing, the resulting carbon yarn product is stiff, brittle, weak and is generally not useable or further processible. This has been determined to be caused, it is believed, by bonding between the individual filaments of the yarn. The bonding is likely caused by the reaction of the sizing material between the filaments during carbonization procedures. The sizing material is present on the raw filaments, and it might be intentionally not removed from the filaments or its removal might be non-uniform. In either case, the resulting carbon yarn product is deficient for the reasons as stated hereinabove.
Unfortunately, perchloroethylene and other scouring solvents have come under scrutiny and regulation, and their use has become increasingly undesirable. A need exists therefore, for a flexible and strong carbon yarn which is prepared without a solvent scouring step.